Heart failure (HF) burdens society because of its high prevalence and the exorbitant costs associated with it. The costs are due primarily to repeated hospitalizations, which have been shown to be associated with failed self-care (e.g., medication nonadherence, dietary indiscretions). Interventions intended to improve HF self- care abound, but HF hospitalizations remain exceedingly common, suggesting that important operative factors have not been identified and addressed. The objective of this study is to examine excessive daytime sleepiness (EDS) as a potential contributor to refractory problems with self-care. We hypothesize that EDS impairs cognition, which contributes to failed self-care, poor health-related quality of life (HRQL), and unplanned hospitalizations. A prospective cohort design will be used to test three specific aims: 1) to describe the transient, reversible factors associated with EDS in persons with HF, 2) to establish the longitudinal relationships among EDS, HF self-care, HRQL, and unplanned hospitalization after controlling for HF severity, and 3) to assess cognitive impairment as the mechanism by which EDS influences self-care and outcomes in persons with HF after controlling for HF severity. After excluding HF patients with major depression or severe cognitive impairment, we will identify a cohort with EDS (with and without mild cognitive impairment) and a control group without EDS (with and without mild cognitive impairment) and follow them for six months. Self-care will be assessed rigorously using multiple subjective and objective techniques. All the domains of HRQL will be measured in relation to HF and to EDS. Unplanned hospitalization will be confirmed using hospital records. All participants will have formal ambulatory sleep testing. An important goal is to explore factors that contribute to EDS in persons with HF that can be modified in a future intervention. Towards this end, we will repeatedly gather detailed physiological, clinical, behavioral, and sociodemographic data on treatment changes and naturally occurring events such as increased nocturia to test hypotheses regarding the effect of changes on EDS, cognition, self-care, HRQL, and unplanned hospitalizations. This study will fill a significant gap in knowledge of why self-care remains a challenge for persons with HF. Relevance of this project to the public: The Institute of Medicine has called public attention to the problems associated with inadequate sleep. Sleep problems are now recognized as an important contributor to illness and poor clinical outcomes. This study will expand and link that knowledge to another important public health problem, poor self-care and treatment adherence, which cost our nation millions of dollars annually. This study is expected to expand existing knowledge and clarify our understanding of the mechanisms linking EDS, failed self-care, poor HRQL, and unplanned hospitalizations in persons with heart failure.